The inquest also heard no case of infection by the worm had ever been successfully diagnosed and treated.

The cause of the meningitis, which also killed the donor, was not known before the transplants took place and was only diagnosed after post-mortem examinations on Mr Stuart and Mr Hughes.

Mr Khalid said he had explained to the men that the risk of transmitting meningitis via transplants was low.

He told the inquest: "An opportunity is given to every patient to decline any surgical procedure. It's not forced upon them."

Mr Khalid, a clinical research fellow at the hospital, said he went through the consent procedure with Mr Stuart, 67, of Cardiff, whom he called an intelligent man with a good grasp of the process.

He also said consultant transplant surgeon Argiris Asderakis had told Mr Stuart the donor had received a five-day course of antibiotics prior to his death and there had been a detailed discussion about the risks.

Consent form

The court heard that the risk of meningitis transmission was explained to 42-year-old Mr Hughes, from Bridgend, as being low.

"He [Darren] had full capacity and he understood those risks" said Mr Khalid. "I helped to sit him up to sign that form and I remember it."

He contradicted evidence from Mr Hughes's father Ian, who had previously told the inquest he had signed the consent form on his son's behalf as Mr Hughes's neurological condition prevented him from doing it himself.

Mr Khalid said: "Darren did sign the form; he did struggle. There's no issue in surgery if a patient can't sign; for example, we often get patients who are partially-sighted or blind."

'Full capacity'

He told the inquest that if Mr Hughes could not have signed the form, he would have asked a witness to sign on his behalf.

Mr Khalid said Mr Hughes had also signed a consent form for his research study the following day, and he did not recall his father being there at that time.

When family members of Mr Hughes were handed copies of the form in the public gallery, they said: "That's not his signature".